Lecture 5 - 2/15/10 The
Urinary
System 
 Chapter
16...

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Unformatted text preview: 2/15/10 The
Urinary
System 
 Chapter
16 
 The
Urinary
System 
 The
urinary
system

 –  excretes
aqueous
waste

 –  maintains
fluid
balance
 –  regulates
blood
composi5on
and
volume
 –  helps
maintain
blood
pressure
 –  monitors
and
maintains
red
blood
cell
levels
 –  assists
in
vitamin
D
synthesis

 –  monitors
and
adjusts
the
ionic
composi5on
of
the
blood
 –  regulates
the
pH
of
the
blood
 –  maintains
blood
glucose
levels
 –  produces
hormones
that
regulate
calcium
levels
 ‐



Fist‐sized,
bean‐shaped
organs
 ‐  Covered
with
a
tough
outer
membrane,
the
renal
capsule
 ‐  A
large
renal
artery
enters
the
kidney
at
the
hilus
 –  provides
exit
for
equally
large
renal
vein
(plus
nerves
and
 lympha5c
vessels)
 –  ureters
also
pass
through
the
hilus
 Renal
pyramids
are
cone‐shaped
structures
formed
from
an
 accumula5on
of
collec5ng
ducts
filled
with
urine
 –  all
waste
materials
removed
from
the
blood
by
the
urinary
 system
leave
the
body
in
urine

 The
Kidneys 
 A
quarter
of
the
blood
flow
from
each
heart
beat
is
sent
to
the
kidneys

 Blood
flowing
through
the
kidneys
takes
a
long
and
circuitous
route
 –  blood
enters
the
kidneys
via
the
renal
artery,
which
branches
out
 towards
cortex
 –  It
is
further
divided
into
afferent
arterioles,
efferent
arterioles
and
 capillaries
 –  filtered
blood
winds
its
way
through
the
kidney
through
the
 efferent
arterioles,
where
it
moves
to
capillaries
and
is
then
 collected
by
the
interlobular
veins
 –  pathway
reverses:
finally
leaving
the
kidneys
via
the
renal
vein
 Blood
Flow
Through
The
Kidneys 
 Millions
of
nephrons
 –  each
nephron
filters
a
 por5on
of
the
blood
 that
passes
through
 the
kidney
 The
blood
vessel
leaving
 each
nephron
wind
 around
the
en5re
 nephron,
exi5ng
via
 renal
vein
 –  it
is
here
that
the
 urinary
and
 cardiovascular
 systems
are
linked
 Nephrons 
 The
nephron
is
the
site
of
blood
filtra5on
 –  wastes
are
removed
and
necessary
ions
and
nutrients
are
 returned
to
the
circulatory
system
 The
waste
material
filtered
into
Bowman’s
capsule
remains
in
the
fluid
 within
a
second
part
of
the
nephron:
the
tubule
has
three
sec5ons
 –  the
proximal
convoluted
tubule
(PCT)
 –  a
loop
called
the
loop
of
Henle
 –  a
distal
convoluted
tubule
(DCT)
connected
to
a
collec5ng
duct
 The
tubule
that
extends
from
the
glomerular
capsule
is
the
proximal
 convoluted
tubule
 One
collec5ng
duct
gathers
newly
formed
urine
from
a
series
of
 nephrons
and
drains
it
to
the
renal
pelvis
 Nephrons 
 1 2/15/10 Nephrons 
 The
body
is
well
supplied
with
nephrons
 The
loop
of
the
nephron
and
the
collec5ng
duct
remove
even
 more
water
from
the
filtrate,
serving
to
precisely
regulate
 fluid
loss
 The
body
maintains
more
nephrons
than
it
needs
 –  there
is
enough
filtering
capacity
in
one
kidney
to
provide
 all
the
cleansing
and
monitoring
of
fluid
balance
necessary
 for
life
 Urine
FormaCon 
 Urine
forma5on
begins
in
the
glomerulus
and
is
finalized
in
the
 renal
pelvis,
through
the
processes
of
filtra5on,
ac5ve
 transport,
and
osmosis

 As
blood
passes
through
the
glomerulus
of
the
nephron,
most
of
 the
liquid
is
forced
out
of
the
arteriole
and
into
the
lumen
of
 the
nephron

 –  this
first
step
of
urine
forma5on
is
termed
glomerular
 filtra5on
 –  water,
nitrogenous
wastes,
nutrients,
and
salts
are
all
 forced
from
the
blood
at
this
point
 Urine
FormaCon 
 Glomerular
FiltraCon 
 Glomerular
filtra5on
is
the
first
step
in
urine
forma5on
 Three
criteria
must
be
met
in
order
to
filter
blood
plasma
through
the
 glomerulus
 –  blood
pressure
must
be
high
enough
to
force
plasma
out
of
the
 glomerular
vessel
walls
 –  the
fluid
already
in
the
glomerulus
must
have
a
low
enough
pressure
 to
allow
more
fluid
to
be
forced
into
the
nephron
tubules
 –  the
osmo5c
pressure
of
blood
in
the
peritubular
capillaries
must
be
 high
enough
to
draw
water
back
into
the
capillaries
from
the
nephron
 tubule
 If
these
condi5ons
are
not
met,
the
nephron
cannot
filter
the
blood,
and
 the
urinary
system
will
fail
 Glomerular
FiltraCon 
 Glomerular
FiltraCon 
 Glomerular
blood
pressure
is
higher
than
systolic
blood
pressure

 –  this
is
caused
by
the
kinking
and
twis5ng
of
the
glomerular
vessels
 The
incoming
(afferent)
arterioles
have
a
larger
diameter
than
the
outgoing
(efferent)
 glomerular
arterioles
 –  this
increases
pressure
in
the
glomerulus
by
crea5ng
back
pressure
 –  the
total
pressure
on
the
blood
forces
most
of
the
fluid
into
the
capsule

 To
filter
the
blood,
the
blood
pressure
must
overcome
the
pressure
of
the
fluid
already
in
 the
capsule
(capsular
pressure)
as
well
as
the
osmo5c
pressure
of
the
blood
itself
 If
your
systolic
pressure
drops
below
60
millimeters
Hg,
blood
in
the
glomerulus
will
not
be
 forced
through
the
glomerular
wall
because
glomerular
pressure
will
not
rise
high
 enough
to
force
plasma
from
the
blood
vessels
 Every
day,
approximately
180
liters
of
fluid
are
filtered
from
the
blood,
but
only
a
small
 frac5on
of
that
is
excreted

 2 2/15/10 Tubular
ReabsorpCon 
 As
filtrate
passes
through
the
nephron,
ions
and
water
are
returned
to
 the
peritubular
capillaries
in
a
process
called
tubular
reabsorp5on,
 the
second
step
in
urine
forma5on

 –  approximately
80%
of
the
filtered
water
is
returned
to
the
blood
 immediately
at
the
PCT
 The
cells
that
line
the
PCT
are
covered
with
microvilli
 –  these
cells
are
adjacent
to
the
endothelial
cells
of
the
 peritubular
capillaries,
crea5ng
a
thin
layer
that
allows
diffusion
 from
the
tubule
to
the
blood
 Essen5al
ions
and
water
are
sent
back
to
the
blood
via
osmosis
and
 diffusion
 –  glucose
returns
using
facilitated
diffusion
 Tubular
SecreCon 
 Tubular
secre5on
is
the
third
step
in
urine
forma5on

 –  it
requires
ATP,
and
provides
delicate
control
over
fluid
homeostasis
 –  it
removes
waste
products
and
other
unwanted
substances
too
large
 to
filter
from
the
blood
at
the
glomerulus
 •  such
as
steroids
and
drug
breakdown
products
 Urine 
 Once
the
filtrate
has
passed
through
the
nephron
and
collec5ng
ducts
and
 reaches
the
renal
pelvis,
it
is
finally
referred
to
as
urine
 While
in
therenal
pelvis,
water
can
con5nue
to
leave
the
urine,
concentra5ng
 the
salts
in
the
urine,
which
can
lead
to
the
forma5on
of
kidney
stones
 –  these
rock‐like
masses,
usually
composed
of
calcium
oxalate,
can
grow
 large
enough
to
block
renal
flow
 Ureters
and
Urinary
Bladder 
 From
the
renal
pelvis,
urine
travels
down
the
ureters
to
the
urinary
bladder
 The
urinary
bladder
is
a
hollow,
variable‐sized
organ
 –  it
is
lined
with
transi5onal
epithelium
to
allow
for
expansion
without
 tearing
or
destroying
the
integrity
of
the
inner
lining
 Discharging
urine
from
the
bladder
is
called
urina5ng,
voiding,
or
micturi5on
 –  this
reflex
involves
both
smooth
and
skeletal
muscles
 When
micturi5on
occurs,
the
urine
leaves
the
body
via
the
urethra
 –  a
single
tube
extending
from
the
trigone
of
the
bladder
to
the
exterior
 Ureters
and
Urinary
Bladder 
 Water‐Salt
Balance 
 Key
func5ons
of
the
kidneys
include

 –  maintaining

the
body's
water
and
salt
balance
 –  removing
acidic
and
basic
substances
from
the
blood

 –  we
excrete
or
reabsorb
many
substances
in
an
effort
to
keep
our
blood
volume
rela5vely
 constant,
and
our
blood
pH
at
roughly
7.4
 The
urinary
system
maintains
the
body’s
water‐salt
balance
 –  excreted
urine
usually
has
a
much
different
osmolarity
than
the
blood
 Dilute
urine
is
produced
by
removing
solutes
from
the
forming
urine
leaving
the
nephron

 –  water
does
not
rou5nely
pass
back
to
the
bloodstream
across
the
walls
of
the
DCT
or
the
 collec5ng
tubule
 –  as
the
ion
concentra5on
drops
in
the
urine,
the
water
propor5on
increases,
so
fluid
reaching
 the
collec5ng
duct
is
far
less
concentrated
than
blood
plasma,
resul5ng
in
dilute
urine
 Concentrated
urine
is
produced
by
the
reabsorp5on
of
water
at
the
loop
of
the
nephron
and
the
 collec5ng
duct
 –  the
cells
of
the
DCT
can
be
controlled
to
reabsorb
water
by
the
presence
of
certain
hormones

 –  water
can
also
be
reabsorbed
across
the
walls
of
the
urinary
bladder
 –  this
reabsorp5on
explains
why
the
first
morning
urina5on
is
more
concentrated
than
urine
 produced
and
passed
later
in
the
day
 3 2/15/10 Urine 
 Chemical
analysis
of
urine
can
 reveal
a
number
of
serious
 diseases
 Because
urine
is
the
by‐product
of
 filtered
blood,
any
unusual
 compounds
or
incorrect
levels
 of
normal
blood
cons5tuents
 will
appear
in
the
urine
 Abnormal
components
in
urine
can
 include
albumin,
hemoglobin,
 red
blood
cells,
white
blood
 cells,
glucose,
and
casts
 –  each
can
indicate
a
specific
 problem
 Albumin
is
a
small
protein
that,
if
present
in
the
urine,
must
be
entering
 the
nephrons
at
the
glomerulus
 Hemoglobin
indicates
bleeding
in
the
upper
urinary
tract
 White
blood
cells
in
the
urine
indicate
that
an
immune
response
is
 occurring
 Glucose
in
the
urine
signifies
diabetes
mellitus
 Casts
are
plugs
of
material,
shaped
like
the
nephron
tubules,
that
build
 up
in
the
tubules
and
then
get
forced
out
by
pressure
 Abnormal
ConsCtuents
of
Urine 
 Kidney
Disease 
 Without
func5oning
kidneys,
blood
composi5on
cannot
be
maintained
and
 homeostasis
will
belost
 •  in
severe
cases,
the
pa5ent
may
require
dialysis
or
even
a
kidney
 transplant
 4 ...
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